Fault resilience for MPLS multicast is becoming increasingly important as revenue generating multicast based business services such as IPTV and virtual private LAN services (VPLS) are being offered over the emerging MPLS based network infrastructure. Fault resilience has traditionally been achieved through protection and recovery mechanisms for link and/or node failures in a network. Such mechanisms in SONET/SDH networks have gained a reputation to be the best in the industry. Realizing a comparable reputation for fault resilience in the emerging MPLS based network infrastructure continues to be an area of active interest.
A connection in an MPLS network corresponds to a label switched path (LSP) and the goal of protection is to ensure that each LSP being protected (referred to as a primary LSP) continues to offer uninterrupted service in the event of any link or node failures. Such uninterrupted service is typically achieved through provisioning of one or more alternate LSPs such that, for each failure of the primary LSP, one of these alternate LSPs remains unaffected and can be activated if not already active.
MPLS fast reroute (FRR) has evolved as the de facto standard protection mechanism for LSPs with a single source and single destination (also known as Point-to-Point or P2P). In FRR, an alternate LSP, referred to as a detour, is established for each LSP segment that needs protection. The node at the beginning of this segment is referred to as the point of local repair (PLR) and the node at the end of this segment is referred to as the merge point (MP). A detour is typically routed along the shortest path (link/node disjoint from the path along the primary LSP) from the PLR to the MP. When a PLR detects a failure, it switches the traffic onto the detour protecting the failed segment and the MP simply merges the traffic from the segment and the detour. The recovery time, which is the time between the occurrence of a failure to the point when the associated detour is activated depends largely on the time it takes the PLR to detect a failure. If the segments to be protected are selected in such a way that the PLR for each segment can detect failures as fast as possible, then FRR can offer recovery times comparable to that in SONET/SDH networks. For example, if every link is protected, then link failure detection is entirely local to the PLR.
The management and signaling of detours for all the LSPs in a network, especially in the event of topological changes can become very complex and computationally burdensome on the network nodes. To alleviate such complexity, a variant known as facility protection is used where segments to be protected are defined along the network topology as opposed to each individual primary LSP and facility detours are created for such segments. Then, any primary LSP traversing a segment with a facility detour has its detour tunneled through the facility detour. Facility detours can be setup to protect links and/or network nodes.
To accommodate the increasing use of MPLS multicast, FRR is now being extended to support multicast LSPs with a single source and multiple destinations (also known as Point-to-Multi-Point or P2MP). FRR for P2MP LSPs, however, can be quite inefficient in terms of the bandwidth it consumes in the network and can involve even more signaling and management complexity due to the increased number of detours especially with dynamic changes in the set of destination nodes or in the event of topology changes. In FRR for P2P, at any given point in time, only one of the primary LSP or its detours can be active on a link.
In FRR for P2MP, however, given that there may be more than one destination node, a detour and the primary LSP may be simultaneously active on a given link. This can cause two copies of the same packet to be sent over such a link. The term packet duplication describes a situation where two or more copies of the same packet need to be sent on a link. Use of P2MP detours can cap the maximum number of copies sent on a link to two, but this comes at a cost of substantially increased signaling complexity or at a cost of wasteful bandwidth consumption, depending on how it is implemented.
These problems of FRR can get significantly magnified for high bandwidth multicast LSPs such as those used to carry IPTV content.
Therefore, it would be desirable to have a method of providing MPLS link and node protection which would not incur the expense and complications of protection as available in the prior art.